Electric discharge apparatus



w. J. 'scoTT ET AL 2,298,904

ELECTRIC DISCHARGE APPARATUS Oct. 13, 1942.

Filed Oct. 1, 1940 Fig.2

Inventors: William J.Sc:otc

Leonard J. Davies,

Their Attorney.

Patented Oct. 13,, 1942 UNITED v STATE ELECTRIC DISCHARGE APPARATUS William J. Scott and Leonard J. Davies, Rugby,

England, assignors to General Electric pany, a corporation of New York s PATENT o Fics 3 Com- Application October 1, 1940, Serial No. 359,254

In Great Britain March 19, 194i) 4 (flaims. (Cl. 176-124) Our invention relates to electric discharge apparatus including a discharge device having spaced-electrodes at least one of which is arranged to be directly heated .by the passage of current therethrough for initially raising its temperature. With the common circuit arrangement wherein the operating current for the device is supplied to such an electrode by a connection with one terminal only thereof it has been found that because of the resistance of the electrode there has been an objectionably unequal distribution of the operating current therein '50 that substantially only that half of the electrode adjacent said connecting terminal is effective as a cathode. It is the obje t of our invention to provide an improved arrangement by which this objectionis avoided.

Our invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed 'out in the appended claims.

Referring to the drawing, Fig. 1 is a circuit diagram of one embodiment of our invention and Fig. 2 showsa detail of the thermal switch employed therein. v

In Fig. 1, we have represented the electric discharge device by way of example as a well-known form of "discharge lamp of the positive column type. As shown the device comprises the envelope I having therein the spaced filamentary electrodes 2, each electrode being attached at its ends to the electrode supporting terminal leads 3 and 4. The envelope may contain a suitable gas or vapor, such as mercury, and the inside surface may, if desired, be coated with a suitable phosphor or produce fluorescence. One nd of each electrode connects with the source 5 of alternating current which for example, may be a 115 volt, 60 cycle lighting circuit. One of thesecon- 'nections is shown including the control switch 6 and the other connection is shown including the ballast reactor 1.' For the purpose of initially raising the temperature of the electrodes to a point of electron emission th other ends of the electrodes are connected together ,through'the starting switch 8. This switch may, ifdesired',

be a hand operatedswitch but preferably is operated automatically with a time delay such that it is not opened until the electrodes have reached an electron emitting'temperature. During the normal running of the lamp the switch 8 will of course remain open. l .7

With the lamp so connected j to the source oi.

current supply those portions of the electrodes .which are nearest to the connections leading to the source are effective as cathodes whereas the portions-remote from those'connections or near the other ends are substantially ineffective as such. In order to produce a better distribution of operating current supply to the electrodes, we

have provided the temperature responsive switch {which in its closed position serves to short circuit the electrode with which it is associated.

This switch which preferably is arranged within the envelope may, for example, comprise a bimetallic element shown in greater detail by Fig.

2 where it is represented as having one end secured to the electrode supporting terminal 4 and the other end'adapted to make contact with the lamp is coolthe bimetallic switch is in open circuit position. When the lamp is in operation,

however, the heat received by the switch from the discharge and from the adjacent electrode is sufficient to warp the switch to its closed circuit position whereby current is supplied to the electrode from both ends instead of at one end as heretofore. Thus, the ntire electrode becomes electron emissive during the normal operarect current a resistive ballast would be employed instead of a reactive ballast as shown.

What we claim as new and desire to secure by Letters Patent of the United States is: i 0

' appreciable amount of resistance, means for connecting said electrodes with a source of current supply to energize the device and initially to heat said one electrode by the passage of heating. current therethrough, and means responsive to heat produced by said device for short-circuiting saidone electrode.

2. In combination, an electric discharge device having spaced electrodes, one of said electrodes having a. filamentary form, means for connecting saidelectrodes with a source of current supply to energize the device and initially to heat said electrode by the passage of current therethrough,

and a thermal switch responsive to heat proother electrode supporting terminal 3. When the tion of the lamp and the objectionable inequality derstood that where the lamp is'operated on di- 1. In combination, an electric discharge device having spaced electrodes, one of which has an 2 essence duced by the device for shunting said filamentary electrode.

3. In combination, an electric discharge device having spaced electrodes comprising an enclosing envelope having spaced filamentary electrodes therein arranged to be initially heated by passing a current therethrough, each of said electrodes having terminal leads secured in said envelope and a thermal switch associated with each electrode and arranged within the envelope for electrically connecting together the leads of each electrode.

4. In combination, an electric discharge device 10 that electrode.

WILLIAM J. scorn LEONARD J. pavms. 

